1. Field of the Invention
The present invention generally relates to the field of patterned structures of semiconductor devices, and more particularly, to a patterned structure with sub-lithographic features and a fabrication method thereof.
2. Description of the Prior Art
With the trend in the industry being towards scaling down the size of metal oxide semiconductor transistors (MOS), three-dimensional or non-planar transistor technology, such as fin field effect transistor technology (Fin FET) has been developed to replace planar MOS transistors. In current techniques, in order to meet the sub-lithographic features, a regular photolithography and an etching process accompanied with a pull back process are provided to form fin structures in the Fin FET. Additionally, semiconductor device manufacturers also utilize a pattern transfer technique, such as sidewall image transfer (SIT) to form required fin structures.
In general, SIT may include the following steps. First, a plurality of dummy patterns is formed on a substrate, wherein the dimension of the dummy patterns is larger than the sub-lithographic features. Next, spacers are formed on the sidewalls of the dummy patterns through a deposition and an etching process. Since the dimension of the spacers may have the sub-lithographic features, patterns of the spacers may be transfer into the substrate by using the spacers as mask. However, this method has it limits and drawbacks, such as all of the spacers can only have the same width. This phenomenon will restrict the applicability of the SIT technique. For example, in static random access memory (SRAM), the layout of spacers is used to define the shape and width of carrier channels. Since the ratio between certain channels will influence the value of static noise margin (SNM) of the SRAM, the value of SNM can not be increased successively in the conventional SIT technique with all of the spacers have the same widths.
In order to overcome the above-mentioned drawbacks, there is a need to provide patterned structures and a novel fabrication method thereof so that the patterned structures with sub-lithographic features can have variable width through a simple and convenient way.